The present invention relates to a valve element as defined in the preamble of claim 1, which comprises a frame, at least one inlet and at least one outlet, a passage connecting the inlet and outlet and at least one burst disk (rupture disk) or equivalent, which, when unbroken, closes the passage from inlet to outlet, and a piston element provided with a piercing element or the like for piercing the burst disk.
A device corresponding to the subject of the invention is known from specification DE 2635076 A. One of the drawbacks of this solution is that the piercing element is returned by the action of pressure back to its original position, so a piece of the burst disk that may have been detached from it by the piercing action may partially block the passage and thus form an obstacle to the flow of pressure medium. In addition, the piercing element has to go completely through the burst disk in order to produce a hole of the desired size in the disk. If the piercing movement is for some reason incompletely executed, it will not produce a hole of the desired size.
The object of the present invention is to achieve a completely new type of solution that makes it possible to avoid the drawbacks of prior-art devices. The object of the invention is to create a reliable apparatus that can be utilized especially in fire extinguishing applications.
The apparatus of the invention is characterized in that the piston element is provided with a passage for a pressure medium, said passage extending axially through the piston element from one first side to one second side, which passage leading through the piston forms a part of the passage of the pressure medium after the burst disk has been pierced.
The apparatus of the invention is additionally characterized by what is stated in claims 2–7.
The solution of the invention has numerous significant advantages. The passage through the piston ensures that the piston will be effectively pressed towards the burst disk after the disk has been pierced even in cases where a higher pressure prevails on the opposite side of the burst disk than on the side of the piston-piercer combination. The solution of the invention is leak-proof and reliable. By making the channel formed through the piston element a part of the passage for the pressure medium, a passage having a constant diameter in all circumstances is achieved.